Problem: Simplify the following expression: ${2a-15+8a-6}$
Explanation: Rewrite the expression to group the ${a}$ terms and numeric terms: $ {2a + 8a} {-15 - 6}$ Combine the ${a}$ terms: $ {10a} {-15 - 6}$ Combine the numeric terms: $ {10a} {-21}$ The simplified expression is $10a-21$